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Please help me now urgent 93 Show that any positive odd integer is of the form 8q + 1 or 8q + 3 or 8q + 5 or 8q + 7 where q is some integer. [CBSE 2012]

Solution-

On dividing p by 8.

Let the quotient be q and remainder be r.

By Euclid's division lemma-

p = 8q+r where 0?r
Varying values of 'r' can be 0,1,2,3,4,5,6 and 7.

When r= 0, p= 8q;r=1, p= 8q+1
r= 2, p= 8q+2;r= 3, p= 8q+3
r= 4, p= 8q+4;r= 5, p= 8q+5
r= 6, p= 8q+6;r=7, p= 8q+7

Clearly, 8q , 8q+2, 8q+4, 8q+6 are even since p is odd so p? 8q , 8q+2, 8q+4, 8q+6.

p = 8q+1 or 8q+3 or 8q+5 or 8q+7 for some integer p.

Hope it helps ~~
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Correction in 4th step.

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  • 3
let a be any positive integer
and b=8
By EUCLID'S DIVISION ALGORITHM,
a=bq+r
so a=8q+0
      a=8q
    a=2(4q)
SINCE 2 IS A FACTOR OF THE ABOVE NUMBER ITS AN EVEN NUMBER
  2ND CASE:
a=8q+1
SINCE 8q IS EVEN WHICH IS PROVED FROM ABOVE, THEN WE KNOW THAT:
EVEN NUMBER+1==ODD NUMBER 
Hence a=8q+1 is ODD
3RD CASE 
a=8q+2
a=2(4q+1)
SINCE 2 IS A FACTOR OF THE NUMBER ITS CONSIDERED EVEN 
4TH CASE
a=8q+3
a=8q+2+1
a=(8q+2)+1
SINCE 8q IS EVEN WHICH IS PROVED FROM ABOVE, THEN WE KNOW THAT:
EVEN NUMBER+1==ODD NUMBER 
SINCE 2 IS A FACTOR OF THE NUMBER ITS CONSIDERED EVEN 
4TH CASE 
a=8q+4
a=2(4q+2)
SINCE 2 IS A FACTOR OF THE NUMBER ITS CONSIDERED EVEN.
5TH CASE 
a=8q+5
a=8q+4+1
a=(8q+4)+1
SINCE 8q+4 IS EVEN WHICH IS PROVED FROM ABOVE, THEN WE KNOW THAT:
EVEN NUMBER+1==ODD NUMBER 
 
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BY ECLUIT GEOMEATRY LEMMA 
8Q+OR 8Q+2 TO 8Q+5 

HENCE OF ECCLUID GEOMEATRY ALL ARE ODD INTEGERS ARE 8Q+1 TO 8Q+7

IF ALL ARE  ODD INTEGERS
SO,ODD INTEGERS CANNOT BE A 8Q,8Q+2,8Q+4,8Q+6
AND 
ODD INTEGERS CAN BE ONLY 8Q+1,8Q+3,8Q+5,8Q+7
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